David Hume (1711–1776)

A Treatise of Human Nature, Book III: “Of Morals”

An Enquiry Concerning the Principles of Morals

Summary

Hume begins by noting the difference between impressions
and ideas. Impressions come through our senses, emotions, and other mental
phenomena, whereas ideas are thoughts, beliefs, or memories that
we connect to our impressions. We construct ideas from simple impressions
in three ways: resemblance, contiguity, and cause and effect.

Next, Hume distinguishes between relations of ideas and
matters of fact. Relations of ideas are usually mathematical truths,
so we cannot negate them without creating a contradiction. Matters
of fact are the more common truths we learn through our experiences. We
understand matters of fact according to causation, or cause and effect,
such that our experience of one event leads us to assume an unobserved
cause. But Hume argues that assumptions of cause and effect between
two events are not necessarily real or true. It is possible to deny
causal connections without contradiction because causal connections
are assumptions not subject to reason.

We cannot justify our assumptions about the future based
on past experience unless there is a law that the future will always resemble
the past. No such law exists. We can deny the relationship without
contradiction and we cannot justify it with experience. Therefore,
we have no rational support for believing in causation. Hume suggests
that our assumptions are based on habit, not reason, and that, ultimately,
our assumptions about matters of fact are based in probability.
If experience teaches us that two events occur together repeatedly,
we will assume a link between them. So, Hume explains, we must be
able to reduce all meaningful concepts to the simple impressions
on which they are built. Since no simple impression of causation
or necessary connection exists, these concepts might appear meaningless.
Rather than dismiss these assumed connections entirely, however,
Hume acknowledges their usefulness and limits them to being nothing
more than simple observations of repeated conjunction between two
events. Further, he concludes that if there is no cause and effect,
then our actions are not predetermined, and we enjoy true free will.

At the end of the Enquiry, Hume pursues
a number of tangential discussions. He argues that humans and animals
possess similar capacities and methods for reason. He denies that
any rational justification exists for belief in either miracles
or most forms of religious and metaphysical philosophy. Although
we can rationally justify our skepticism regarding the existence
of an external world, that doubt destroys our ability to act or
judge. The instinctual beliefs formed by custom help us get along
in the world. As long as we restrict our thinking to relations of
ideas and matters of fact, we are acting within the limits of reason,
but we should abandon all metaphysical speculations as useless,
impossible to resolve, and nonsensical.

Analysis

Hume seeks to explain our understanding of the world rather
than try to justify our beliefs or prove anything. Here, he does
not address the existence of necessary connections between events
but states merely that we cannot know what those connections are.
Ultimately, Hume argues for a mitigated skepticism. We have no good reason
to believe much of what we believe about the world, but human nature
helps us function in all the ways that reason cannot. However, we
must limit ourselves by accepting that matters of fact are our sole
source of true information. If past experience cannot teach us about
the future, it becomes difficult to function on a practical level.
The elimination of causation would make it impossible for us to
function, if it meant that we began to act as if causation didn’t
exist. Whether or not we can know of a necessary
connection between two events is not worth arguing about. Similarly,
Hume does not think we should spend time and energy on questions
such as whether God exists, what the soul is, or whether the soul
is immortal. He claims that because the mind is not meant to help
us discover and define truths, we will never be able to come to
any definite and rational conclusions about abstract matters.

Hume is skeptical about his own explanation of why we
cannot rationally make necessary connections between two events.
He stops short of saying that it is impossible to predict future
events based on past experience and explains only that we lack any
solid reason to believe this is the case. Hume admits that, if we
observe that one event repeatedly follows another, it is natural
that we assume the two events will always occur together in this
pattern. He also admits that we must necessarily make such assumptions
to live our lives. Such assumptions are practical and useful but
not completely reliable or passable as proof. We are wrong to justify
these beliefs by claiming that reason supports them or that we can
absolutely know that one event causes the other.